New commercial crew spacecraft for the International Space Station will be able to do more than just carry astronauts to the orbiting lab: They will also serve as temporary shelters, or even fly crew home, if there is an emergency in space, according to NASA.

Currently, in dangerous situations, such as when a piece of orbital debris threatens the space station, crewmembers take shelter in the Russian Soyuz spacecraft. And if a medical emergency were to arise that could not be handled in orbit, the crew would head back to Earth in the Soyuz craft.

"The scenarios that would call for the spacecraft to operate as space-borne lifeboats have not occurred on the International Space Station before, but mission planners have long made sure they are prepared," NASA officials added.

"An electrical issue or ammonia leak on the space station could call for astronauts to shelter inside a Commercial Crew Program spacecraft long enough to correct the problem."

Today, the space station typically has six people on board, made up of two separate Soyuz crews, although the number sometimes reaches nine. Each person has an assigned emergency seat that he or she would use if the need were to arise. Therefore, the number of emergency seats limits how many people can be on the spacecraft at one time.

The Russian Soyuz can seat up to three people at a time. Depending on the crew configuration, the Dragon and CST-100 vehicles will each seat up to seven crewmembers.

However, the new spacecraft must meet a strict list of NASA requirements to serve as a lifeboat. Specifically, NASA said the spacecraft must be able to turn on quickly, even after sitting dormant at a docking station for weeks or months.

"Some systems will take longer to bring online, but the idea is to have spacecraft that astronauts can get into quickly for survival and then use to pull away from the station and come home if that is needed," Kathy Lueders, manager of NASA's Commercial Crew Program, said in the statement. "Defining exactly what that means, and what the companies can do to make it real, was the hard part. That's why we took a teamwork approach from the start and why we've treated this as a partnership."

Both Boeing and SpaceX are performing Earth-based tests of their spacecraft before doing in-orbit evaluations with a crew on board. After that, they will test their spacecraft's capabilities during a short mission.

"Their performances in space — without an actual emergency — are to be considered carefully before NASA certifies the companies to fly operational missions, which could see a spacecraft docked to the station for months at a time," agency officials added.